Heavy oils and bitumens make up an increasing percentage of hydrocarbon resources. As the demand for hydrocarbon-based fuels has increased, a corresponding need has developed for improved processes for desulfurizing oil feed streams. Processes for the conversion of the heavy portions of these feed streams into more valuable, lighter fuel products have also taken on greater importance. These heavy oil feed streams include, but are not limited to, whole and reduced petroleum crudes, shale oils, coal liquids, atmospheric and vacuum residua, asphaltene, de-asphalted oils, cycle oils, FCC tower bottoms, gas oils, including atmospheric and vacuum gas oils and coker gas oils, light to heavy distillates including raw virgin distillates, hydrocrackers, hydrotreated oils, dewaxed oils, slack waxes, raffinates, and mixtures thereof.
Hydrocarbon streams having a boiling point above 220° C. often contain a considerable amount of large multi-ring hydrocarbon molecules and/or a conglomerated association of large molecules. These larger molecules and conglomerations often contain a large portion of the sulfur, nitrogen and metals in the hydrocarbon stream, which may be referred to as heteroatom contaminants in U.S. Pat. No. 8,764,973 to Litz et al., the contents of which are hereby incorporated by reference in its entirety, except where inconsistent with the content of the current disclosure. A significant portion of the sulfur contained in these heavy oils is in the form of heteroatoms in polycyclic aromatic molecules, comprised of sulfur compounds such as dibenzothiophenes, from which the sulfur is difficult to remove.
The processing of bitumens, crude oils, or other heavy oils with large numbers of multi-ring aromatics and/or asphaltenes can pose a variety of challenges. Conventional hydroprocessing methods can be effective at improving API for a heavy oil feed, but the hydrogen consumption can be substantial. Conversion of the liquid to less valuable products, such as coke, can be another concern with conventional techniques. Desulfurizing techniques and systems which have been disclosed by others including those systems described in U.S. Pat. No. 8,894,845 to Vann et al., U.S. Pat. No. 8,696,890 to Soto et al. and U.S. Pat. No. 8,673,132 to Leta et al., react unoxidized sulfur at high temperatures to cause thermal cracking reactions in oil. Cracking reactions convert unoxidized sulfur compounds to H2S, resulting in the production of olefins and increases in the aromaticity which may be undesirable.
There is thus a need for a system and method for desulfurization that is capable of at least one of removing oxidized sulfur containing compounds such as sulfones, operating at lower temperatures to avoid thermal cracking reactions, producing non-ionizable hydrocarbon products while having reactants that are easily regenerated in-situ.